It is known that hydrogels have shown promise in many applications, mainly due to their high water content and rubbery or pliable nature, which can mimic natural tissue and can facilitate the release of bioactive substances at a desired physiological site. While the hydrogels generally have the above mentioned beneficial properties, the gel tends to shrink with time at it release the entrapped water. Therefore, the hydrogel has not only poor formulation stability but, when such a hydrogel preparation is applied to the skin, it's elicits irritable response owing to vaporization of entrapped water. Inorganic gels are well known and have long been used for various purposes, for example, for the adsorption of condensable vapors from gaseous carriers and for catalytic purposes either as a catalyst itself or as a component there of or as a carrier.
U.S. Pat. No. 5,069,816, entitled “Zirconium Silica Hydrogel Composition and Method of Preparation” wherein the methods for producing zirconium hydrophilic and hydrophobic silica hydrogel is reported. The preparations of these silica hydrogels require elevated temperature of about 800 to 1200° C. and also require elevated pressure from 100 to 500 psi. The main drawback of the given reference is towards the formation of hydrophilic and hydrophobic silica gel in the drastic conditions such as higher temperature and higher pressure applied.
U.S. Pat. No. 6,239,243 entitled “Method for Preparing Hydrophilic Silica Gels with High Pore Volume” wherein it has been reported for the preparation of hydrophilic silica hydrosol (SiO2). The overall process requires elevated temperature from 90° C. to 800° C. to make the hydrophilic silica gels. The drawback of the given reference is the use of elevated temperature that should be attained under oxidizing atmosphere.
U.S. Pat. No. 4,169,926 entitled “Inorganic Hydrogels and Uses Thereof” wherein it has been reported for the preparation of silica-containing hydrogel with contacting agents comprising oxygen-containing organic compounds for catalytic purposes employing well known prior art, e.g., such as that disclosed in U.S. Pat. No. 3,887,494. In this invention titanium tetrachloride was incorporated for the preparation of inorganic hydrogels. The major drawback of this invention is the use of titanium tetrachloride which is a highly toxic and corrosive substance. On accidental release, it creates liquid pools that can either boil or evaporate.
Reference may be made to the Journal “Needle-Shape Crystal of Sodium Chloride Obtained by percrystallization” (Journal of American Chemical Society 54, 1932, p 2392), wherein it is reported that the needle like sodium chloride crystal appear in collodion bag. Further author was speculated by this method would afford a practical way of getting rid of the inorganic diffusible salts and at the same time concentrating the enzyme. Disadvantage: The involvement of sodium chloride forced for percrystallization is devoid of any other phenomena and not enough for any successful application of this process.
Reference may be made to patents U.S. Pat. No. 18,160A1 and U.S. Pat. No. 7,347,988, wherein hydrogel with ordered crystalline structure is created. This invention particularly relate to the production of crystalline hydrogel by using a major monomer is N-isopropylacrylamide and co-monomers are hydroxylethyl acrylate, allylamine, acrylic acid and other related analog and solvent is water. Disadvantage: The bottleneck in this procedure is the use of crosslinking agent for the formation of crystalline hydrogel. The pharmaceutical applications relate to the controlled delivery of active compounds for the treatment of a variety of disease requires physiological conditions for biodegradation of such crosslinking agents and to achieve the release of active entrapped compounds.
It is evident from the prior art that there are some limitations with the reported inorganic hydrogels. The preparations of such inorganic hydrogels require drastic conditions to form gels. One such condition is the temperature factor, which is very high in the prior art. Further, it is evident from the prior art that these inorganic hydrogels are not crystalline in nature and the reported crystalline hydrogels are based on organic constituents. In the present invention, we report the formation of inorganic hydrogels under ambient conditions, which can be prepared with great ease without any drastic temperature or pressure. These inorganic hydrogels also have a very special feature of crystalline in nature. The present invention for the formation of inorganic hydrogel is not only limited with sodium chloride, however, it involves other alkali halides from sodium to cesium ions. Several advantages of this invention will be apparent to those skilled in the art upon a study of this disclosure and the appended claims.